The present application is in the field of mobile wireless communication systems, including 3rd generation partnership project (3GPP) Long-Term Evolution Advanced (LTE-A). And in more detail, the problem raised and scheme proposed are particularly relevant for Home eNodeB (HeNB) interference control and self-configuration in dynamic HeNB network.
Self-Organizing Networks (SON) is a distributed way to deal with problems existing in a network, and it has been determined as work item in 3GPP RAN3 [1] and RAN5 [2][3]. Self-tuning is an important part in SON [1][4], and its purpose is to figure out the faults which could be solved automatically by triggering appropriate recovery actions. For example, the “fault” may be mainly focused in the field of spectrum usage.
Due to the scarcity of the spectrum, with the increasing number of HeNB/HNB, some problems, such as strong interference, low throughput, occur in some nodes (say ill HeNBs, otherwise, say healthy HeNBs) in the networks. Self-tuning covers these problems for interference mitigation and throughput improvement. In the process of self-tuning, these ill HeNBs collect information of others and negotiate with them (not excluding negotiating with a network coordinator and some healthy HeNBs).
It can be expected that self-tuning will be a good scheme for HeNB/HNB, and will be a valuable topic in the near future.
It is expected that HeNB will be deployed in large scale. In no doubt, the number and density of HeNB will increase greatly in the coming years, especially in urban areas. On the other hand, the presence of pico cell, relay, etc, will cause the limited spectrum resource becoming scarcer. It can be predicted that spectrum jamming among HeNBs and HeNBs with other network (including pica cell, relay network, etc.) will be a serious problem. The problem will be sure to restrict the deployment of HeNB significantly.
Self-organization and self-configuration are efficient ways to solve the problem. In the following, one example is given.
According to FIG. 1, there are two component carriers (CCs) (CC1 and CC2) at all in the network. HeNB1 chooses CC1 as its active CC, both HeNB2 and HeNB3 use CC2. So there exists serious interference between HeNB2 and HeNB3 in FIG. 1. If one interference coordination mechanism (self-tuning) is available, then HeNB1, HeNB2 and HeNB3 (all, or some of them) could appropriately reselect their active CC, and then the spectrum jamming will be solved (FIG. 2). That is, HeNB1 and HeNB2, which are relatively well separated from each other, may select CC1 as active CC, and HeNB3 may select CC2, or vice versa.
In 3GPP, the topic of self organizing network (SON) has been discussed [1]-[3]. It provides efficient management for a small cell network, which includes numerous cells, such as femtocell (also called home NodeB/home eNodeB, HNB/HeNB). Self-tuning is an important part in the framework of SON [4], and self-tuning process and function have been defined in [2]. Self-tuning in the field of frequency resource optimization or interference management has not been widely discussed. For example, the corresponding use case according to section 4.9 of [1] is not completed.
On the other hand, interference mitigation has been a hot topic in 3GPP RAN4 (RAN: radio access network) work item, frequency division duplex/time division duplex (FDD/TDD) HeNB radio frequency (RF) requirements [5][6]. Sections 7.3.2.2.1 and 7.3.2.2.2 in the text proposal part in [7] conclude solutions for HeNB downlink interference mitigation among neighboring HeNBs. In section 7.3.2.2.1, solutions for centralized network architecture are given, and in section 7.3.2.2.2, solutions for a distributed architecture are provided. In the following, these two solutions are introduced shortly.
Centralized Architecture
In centralized network framework, one centralized controller is need. Each HeNB estimates the fraction of time it needs to transmit according to the traffic load and channel conditions of its UEs, and reports this ratio to the centralized controller via S1 signaling. After receiving the report, the centralized controller forms an adjacency graph of all HeNBs, and then determines the subframes or subbands (carrier frequency) that each HeNB is allowed to transmit, and notifies them of their transmission pattern via S1 signaling [7].
Distributed Architecture
In distributed mode, there is no centralized controller, and one certain HeNB constructs a “Jamming Graph”, which describes the interference relationship between itself and its neighbors. Some examples and algorithms are given in [8]-[10]. Additionally, utility function [11] is needed for each HeNB to make decision on whether to send resource coordination request to its neighbors and whether to agree the request from its neighbors.
Information, such as active CC labels and neighbor HeNBs' ID, should be exchanged among HeNBs.